Updating BBCode highlightjs grammar

[Alteras1]

Rewrites the bbcode grammar to more closely match common bbcode syntax types (see https://www.bbcode.org/reference.php)

• Adds a simple test case
• Includes generated CDN and updated Readme (hopefully addressing Please include both a NPM requirable file and a CDN-ready distributable #2 )

Notes:
I ended up creating the grammar from scratch since I felt the previous grammar didn't cover the different cases I've come across well enough. Every site seems to have a slightly different implementation of bbcode, so I could be totally wrong in my view of the syntax. Thought I'd share and update the grammar (and overall repo) here regardless.

I'm honestly not sure how (or even if) to update author fields and credits, as I feel duplicitous doing a whole rewrite and leaving it under the previous name. I also don't have any concrete intentions to be the maintainer here. If someone from the highlightjs maintainers can help/advise, that'll be great.

[cobaltt7]

FWIW, I originally made this four years ago, more as a way to introduce myself to how GitHub works more than anything else. I honestly don't really care what happens to it at this point. Feel free to remove me from the credits if you'd like